12 Edmund B. Wilson 



a clear and complete view of such a group; but this one case 

 suffices to give, with great probability, the explanation of the 

 increased number of chromosomes. In this case every chro- 

 mosome of the metaphase group may be clearly seen, and the 

 number is exactly twice the oogonial number, namely, forty-four 

 (Fig. 2, ). Careful study clearly shows that this group contains 

 four microchromosomes and eight macrochromosomes, in each 

 case twice the number of those present in the oogonia. This 

 leaves no doubt that in this case all the chromosomes have divided 

 once without the occurrence of a cytoplasmic division, and makes 

 it probable that the increase in number in the cells in question is 

 always due to a process of this kind. I have not been able to 

 obtain faultless preparations of the dividing cells of other tissues, 

 and can only state that in the ectodermal cells of the larva the 

 number of chromosomes is approximately the same as in the 

 oogonia. The multiple chromosome-groups were only observed 

 in the cells mentioned above, all of which, it may be observed, 

 are degenerating or highly specialized cells. 



c. Alydus pilosulus 



Despite the small number of chromosomes ( 9 14, d 1 13, as in 

 Protenor) this genus is in some respects less favorable for detailed 

 analysis than either of the ones described above, for the size of 

 the heterotropic chromosome does not distinguish it sufficiently from 

 the other chromosomes to allow of its certain identification in the 

 spermatogonia. The main fact appears, however, as clearly as 

 in Protenor or Anasa that the female has one more chromosome 

 than the male. 



In polar views of the second spermatocyte-division this species 

 shows the sister spermatid-groups with great beauty, one having 

 six chromosomes and one seven (Fig. 3, ^, /). These chromo- 

 somes show at least five distinguishable sizes that are constant, 

 namely, (i) a largest; (2) an extremely small one (w-chromo- 

 some); (3) a second smallest (the heterotropic); (4) a second 

 largest, and (5) three others intermediate in size between (3) and 

 (4), one of which is frequently a little larger than the other two. 



